Lunch & Learn | Current status of the In-situ interaction experiment at the Bukov URF

Current status of the In-situ interaction experiment at the Bukov URF

Experiment description and operation

One of the most crucial aspects of the development of the future Czech deep geological repository (DGR) for spent nuclear fuel and radioactive waste concerns the comprehensive research programme underway at the Bukov underground research facility (URF). 2017 saw the launch of the Interaction Experiment, the aims of which are to study the interactions between Czech BCV bentonite and concrete at various temperatures (ambient, 100 °C, and 200 °C) within the local rock environment and to examine the stability of the various materials. The experiment consists of five heated and five non-heated physical models installed in horizontal boreholes at the Bukov URF. Each model contains a different combination of materials, including bentonite pellets and compacted bentonite blocks with varying dry densities (1200 and 1600 kg/m³), low pH concrete (LPC), and ordinary Portland cement concrete (OPC). Sensors emplaced within the models serve for monitoring a range of parameters such as the pore water pressure, temperature, total pressure and water content of the bentonite filling material. Mechanical packers and an anchoring system secure the models within the boreholes. In addition, the groundwater obtained from a local source used for the artificial saturation of the models is continuously monitored for its chemical and physical properties. The in-situ experiment, which has been in the loading phase since 2019, is expected to continue until 2026, at which time the final model will be dismantled.

The bentonite used in the experiment, which was sourced from the Černý vrch deposit (BCV_2017) in the Czech Republic, comprises a calcium-magnesium-type bentonite. This bentonite, which is currently considered the reference material for SÚRAO’s buffer and backfill programme, was studied extensively prior to the launch of the experiment, including via research by Svoboda et al. (2022).

Dismantling of the experiment

The dismantling stage of the experiment began in late 2024 and will continue until 2027, including all the analysis work involved and the preparation of the final report. The dismantling process involves the removal of the physical models from the host rock and the conducting of an extensive laboratory programme aimed at the detailed analysis of samples of the materials. The dismantling procedure includes the overcoring of the models using a wire saw and their extraction from the rock mass along with sections of the surrounding rock aimed at preserving the integrity of the samples for the laboratory analysis.

The analysis will provide a detailed insight into the interactions between the materials in the models, specifically the interactions between the rock, cement and the bentonite (in both the block and pellet forms). The primary focus will be on evaluating changes in the physical, mineralogical, geochemical and geotechnical properties of the bentonite and the concrete. In addition, the microbiological analysis will assess the impact of microorganisms on the stability and functionality of the sealing materials intended for the DGR. This research will also investigate the bacterial communities identified and their activity along the interfaces of the materials.